Generally, a motor has been known in which a rotor (rotation member) supported by a support shaft (fixed shaft) is rotationally driven by a magnetic field generated from a drive coil which is disposed on an outer peripheral side of the rotor (see, for example, Patent Reference 1).
An example of the motor (motor 100) is shown in FIG. 6. The motor 100 is structured of a motor main body part 100a and a gear head 100b. A support shaft 104 is fixed to a motor case 102 in which a drive coil 106 and the like structuring the motor main body part 100a are accommodated. A bearing 120 for improving sliding property with respect to the support shaft 104 is press-fitted and fixed to a rotor 110 which is rotatably supported by the support shaft 104.
[Patent Reference 1] Japanese Patent Laid-Open No. Hei 01-152942.
When the motor 100 is driven, the bearing 120 may expand due to frictional heat caused by sliding between the support shaft 104 and the bearing 120, which may cause that an inner diameter of a bearing hole 120a into which the support shaft 104 is inserted becomes larger.
As a result, a clearance between the support shaft 104 and the bearing hole 120a is increased and thus a noise referred to as a so-called “striking noise” is occurred by means of that the support shaft 104 and the inner peripheral face of the bearing hole 120a are hit with each other.